[5] Colfax Township is in central Mecosta County, with Big Rapids, the county seat, 2 miles (3 km) west of the township's western border.

State highway M-20 passes through the center of the township, connecting Big Rapids to the west with Rodney on the eastern edge of the township, then continuing southeast to the village of Mecosta.

The southeast corner of the township drains to the West Branch of the Little Muskegon River.

As of the census[3] of 2000, there were 1,975 people, 734 households, and 566 families residing in the township.

17.7% of all households were made up of individuals, and 5.7% had someone living alone who was 65 years of age or older.